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Millions of moving parts

Think about your lawn (or your neighbors). You may mow, weed, fertilize, pesticide the place to achieve the model Scott’s monoculture, but as soon as you stop, this even, level, uniform space quickly grows in “weed” diversity. If a niche is a special place (like a south-facing, dry, rocky slope), then why do many species move in to occupy this uniform space?

What is an ecological niche in this context? What would the lawn look like in 5 years, and how would you describe and explain its structure? What might trouble you in thinking about niche differentiation and community structure in this lawn?

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5 Responses to “Millions of moving parts”

I am glad you brought this up; because I had a rear lawn that never got the top soil returned to it after the house was built. I tried in vain to grow grass back there, to no avail. I do not believe in chemicals and all of that crap. I had great success with grass and white clover in the front of the house, where it had been top soiled and graded properly, but the disturbed clay in the back was impossible. Vermont is naturally a northern hardwood forest, so a northern hardwood forest is what took over eventually. First there were ground covers; the shorter natives like mullein, vetch and dandelions. Then the taller natives came in. We had a lot of natives with an abundance of sticky seeds, which had obviously been brought in on the coat of wild animals or pets in the neighborhood. The deep roots of the dandelions and the Queen Anne’s lace were beneficial to aerating the dense clay soil, so letting them go a bit was a wise move for the overall health of the little ecosystem that was my lawn. Chicory was another native that was happily resident. Following this invasion small hardwood seedlings began to appear. Some were very fast growing and created a small copse within a season or two. Once that copse got thick enough the ground cover became more algal/lichen and less actual plant varieties. I thought of this as my native species laboratory and was somewhat happy to see what would come up next.

If you think of my disturbed clay soil as a niche, then you can see that the diversity of plant life and the order in which they appeared seemed to renew and reclaim the space as a vital environment that contributed to the well-being of the surrounding native life. Different species came in to thrive at different times based on the conditions present. The low height species contributed to the later well-being of the higher height species by aerating the soil or fixing nitrogen or just creating organic matter that broke up the nasty clay. As the height of the vegetation increased the lower height plants disappeared. Their job was done.

While my lawn began as disturbed clay without topsoil, this is not unlike a chemically treated lawn in that the native environment was badly disturbed by human interference and then turned into an environment harmful to the native broadleaf species killed by the pesticides.

The trouble with thinking about niche differentiation and community structure in this situation is that it is going to be dominated only by native species which are able to thrive in adverse conditions and without the benefit of the complex system of the normal undisturbed environment. Theoretically there will come a time when the disturbed land will be returned to a native condition, but no matter how much it might seem native it will always be lacking in the actual native complexity discussed in the last module subsection.

The question of why so many species move in to occupy the uniform space occupied by a lawn quickly leads me to unscientifically conclude that grass is a weak competitor with little mutualistically beneficial qualities. If the established lawn that dominates many residential landscapes was a strong competitor it seems that it would out-compete newly entering weeds, especially since it has such an initial advantage due to its overwhelming presence, but it does not. It is quickly overtaken and quickly disappears. This seems to indicate that the grass also has little mutuality value. The other weeds entering do not seem to benefit from the ongoing presence of the grass. In addition, the lawn monoculture typically found in residential communities is not established through a process of co-evolution or mutualism so no complex community structure develops. This seems to lead to a lack of stability and resilience. The survival of the grass seems to be dependent upon human intervention such as fertilization. This intervention is designed to create an environment or ecological niche where the grass can thrive while also creating inhospitable conditions for competing species. Once human intervention is removed then the community is no longer ideal for grass and quickly transitions to become desirable for other community members such as weeds that find the resources they need within the ecosystem to rapidly reproduce and dominate a newly available ecological niche. The lawn area will progress through successional change where new plants such as weeds colonize the area and become established which leads to the extinction of much of the formerly dominant grass. This first succession is stimulated by the disturbance resulting from the elimination of continued human intervention in the area through fertilization and mowing the lawn. I would expect in 5 years the area once occupied by the lawn would become a mix of diverse perennial grasses/plants/weeds some of which would grow to be a few feet in height. Over time shrubs and bushes would start to become established followed years later by soft-wood trees and pine bushes, and years later by hard-wood trees.

I wonder what would happen if instead of grass the “lawn” was established with human intervention to support a hardy, perennial plant or “weed”. I think a monoculture weed would face the same successional changes I describe above due to the complexity of the interactions between the “lawn” area and the surrounding ecosystem. Inputs from the surrounding area would be introduced into the area after human intervention is terminated and once the right community member identifies an ecological niche it will take hold, colonize, establish itself, and push out some of the dominant weed causing some of the previous extinction weed in specific sub-set areas of whole lawn area.

I agree with the others that a manicured lawn gives the grass an unnatural advantage over other plants. If left to natural competition, grass is usually pushed out of the environment where native species eventually repopulate. Also with the abundance of nutrients artificially put in the area promotes even more growth of weeds on the lawn. Eventually if no care or maintenance is given to the lawn, various possibilities would happen given the specific orientation and attributes of the location. Trees could grow, animals could set up shop, etc.

The ecological niche in this context can be viewed in term of the grass which does not have an ecological niche in the environment. It is something that is dependent on human interaction. If is very rare to hear of a manicured lawn taking over habitat. Most always it is the complete opposite. So in the context of the weeds, they serve a very important niche in the ecosystem. First off they are native to the given area which already gives them a predisposition to excel in the growing environment of the area. Secondly weeds are diverse and serve as food and habitat for a variety of species. Weeds serve as one of the very important building blocks of the food web. Manicured grass could never fill the niche for all the various weeds in the area. The differentiation that the natives “weeds” give to community structure is invaluable.

When people cultivate their land and yards to grow grass, they are also enriching their land so that other organisms will find the land fertile and desirable. Land that is fertilized to encourage grass will also encourage other “undesirable” plants (read: weeds) to settle their roots in the land.

My family’s vacation home has a small lawn in front of it, but we don’t fertilize it or reseed it – it grows when it wants to grow, and it’s filled with clover and dandelions as well as grass. We probably cut it once every few weeks in the summer. It’s definitely not a monoculture, but it serves the “purpose” of a lawn (nice to walk barefoot on, looks nice…what are the other uses of a lawn?). If we were to do nothing to it, it would become overgrown and meadow-like, and with enough time, it would probably start to grow some bigger plants and trees from seeds that are blown and carried in from the forest surrounding it. It seems to me that the energy (both human-wise and fuel-wise) that it takes to maintain a lawn is kind crazy, and perhaps in a peak-oil world is impossible.

An organism is attracted to choose and remain in a habitat that serves its niche-needs, surrounded by the resources, ecosystem services, and organisms that will contribute to its survival. Organisms may be tempted by a habitat that has a few strong resources that an organism desires but not everything its ideal niche provides, be it enough direct sunlight, high salinity, an abundance of food, or some other resource. Those who are best suited will stay, and those who are not will venture to better places or try to manipulate the environment to serve it better. Just because a habitat may be uniform in its environmental characteristics does not mean it will attract only one sort of organism: different aspects of the habitat will create the “perfect” niche for many organisms. And as more come, the interaction between them (ecology!) will create new, emergent characteristics of the niche. An ecological niche is not only characterized by its physical environment, but the environment that is created by the interactions between all the organisms living there. What may at first be a species’ “fundamental niche,” may need to be fought or negotiated for in order to use the habitat’s resources and not damage the ecosystem services necessary for life.

Niche differentiation will always occur, as long as substantial, concentrated external inputs are not impressed on the system. In an area that is, for example, prone to extremely harsh climates, ice storms, or floods, these frequent environmental disturbances will tend to lessen the diversity and health of the ecosystem. Similarly, constant human inputs such as constant fertilizing, mowing, weeding and reseeding causes the lack of diversity that creates a system very dependant on those external inputs to maintain life as it is desired by humans.

What can we extrapolate from the strength of diversity in natural communities? Does it follow that a community (say, a “homogeneous” wealthy suburbs of white doctors and lawyers) that artificially restricts its population (“weeding” and “fertilizing” in order to cultivate the growth it desires) will suffer from similar weaknesses and a lack of stability because of its lack of diversity?

In the context of the fertilized, well manicured lawn, treated with pesticides, the interventions are designed to favour specific species, and eliminate others. The natural structure of the ecosystem is affected by this “disturbance” to favour the preferred species. Competitors are artificially eliminated, or differentiated through this process as it is artificially supplied with resources to facilitate its growth. This process creates an ecological niche for the preferred species/ organisms within this community. One of the outcomes of this process is that the preferred species becomes stronger than it might under ordinary conditions, allowing it to become a stronger player in the natural selection process, giving it an unnatural advantage. Natural predators are less likely to intervene or survive intervention, and the dominant species is catered to so it can become like a super species, stronger than it would normally be under natural conditions. The artificially maintained ecosystem in lawn supports fewer organisms until such a time when the interference stops. In a five year time frame, with continual protection and intervention, the community would be extremely limited, and it would become a very isolated species with very limited competition or threat.

If however, the intervention was eliminated, and the lawn is left alone, and no further intervention takes place, the lawn will eventually revert to its natural form. The degree of the disturbance would affect how long it would take for the community structure to revert to its natural form, however the process would begin relatively quickly, I would think. I think it could be more at risk than other lawns because it has been artificially maintained and may not have developed the same capacity to compete for space as other similar species that weren’t artificially protected. This may start the process of species differentiation, so you would expect to other types of grass perhaps start to grow. This process would affect the evolution of the community, and would be dependent on the proximity of predators (is the neighbors lawn still being fertilized/ treated/ mowed?) Natural predators may have further to travel, or have limited access to this community, making it more or less vulnerable.